ABSTRACT Androgen receptor (AR) plays a critical role in progression of prostate cancer. We have recently demonstrated that Ack1 (also known as TNK2) regulates AR Tyr267-phosphorylation within the transactivation domain. While AR transcriptional activation by multiple tyrosine kinases is emerging as an alternate mode of AR activation, the precise role of Ack1 mediated AR Tyr267- phosphorylation in AR recruitment to the androgen responsive enhancers (ARE) and androgen- independent AR-responsive gene transcription is not fully understood. In this grant proposal we demonstrate that activated Ack1(pTyr284-Ack1) expression is upregulated as prostate cancer progresses and this activation is inversely correlated with the survival of prostate cancer patients. Since Ack1 regulates androgen-independent AR activity by its phosphorylation at Tyr267, we generated antibodies that specifically recognize pTyr267-AR. Neither pTyr267-AR expression nor its transcriptional activation was affected by anti-androgens e.g. bicalutamide/casodex and flutamide. However, a small molecule inhibitor of Ack1, 4-Amino-5,6- biaryl-furo[2,3-d]pyrimidine (YL3-026) not only inhibited Ack1 activation, but was able to suppress pTyr267-AR phosphorylation, binding to PSA, NKX3.1 and TMPRS2 promoters and inhibit AR transcription activity as seen by significant decrease in PSA gene expression. Our evidence indicates that targeting Ack1 kinase in prostate cancer patients could therefore be highly effective therapeutic strategy. In this proposal we will determine how AR Tyr267- phosphorylation regulates Androgen-Independent growth. Further, we will examine the ability of Ack1 inhibitor, YL3-026, to suppress androgen-independent transcription and xenograft tumor formation. Moreover, we will assess the ability of Ack1 inhibitor YL3-026 to suppress AR Tyr267-phosphorylation and prostatic intraepithelial neoplasia (PINs) formation in Prob-Ack1 transgenic mice.